Multiple-beam klystron apparatus with periodic alternate capacitance loaded waveguide



Aprll 26, 1966 M. RBOYD ET AL 3,248,597

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April 26, 1966 M. R. BOYD ET AL 3,248,597

MULTIPLE-BEAM KLYSTRON APPARATUS WITH PERIODIC ALTERNATE CAPACITANCE LOADED WAVEGUIDE Flled Feb. 16, 1962 2 Sheets-Sheet 2 SUPPLY Fig. 3.

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Theodor-S M/hrdn b 1 The/r Attor-n United States Patent Office 3,248,597 Patented Apr. 26, 1966 MULTIPLE-BEAM KLYSTRON APPARATUS WITH- This invention relates to multiple-beam radio frequency (R.F.) apparatus capable of generating and handling relatively high electromagnetic wave power at relatively high frequencies.

In various systems such as radio communications and radar, operations are limited to a significant extent by the power generating capabilities of the system. The ranges and effectiveness of such systems could, in many cases, be significantly increased by higher power levels of electromagnetic wave energy.

It is further required in systems of the type mentioned that the energy source be stable under various operating and load conditions and it is desirable to achieve relatively high bandwidth and efficiency in such systems.

The klystron type of electron discharge device of present commercially-available construction is a relatively stable source of high frequency electromagnetic wave energy. However, such a device has a limited power handling capability which depends upon factors including the frequency at which the device is operated, cathode emission density and thermal dissipation of various portions of the high frequency circuits. This latter limitation becomes particularly significant in devices operable at relatively high frequencies inasmuch as resonator dimensions are limited to values less than one free space wave length. Also, in order to achieve satisfactory coupling between the electron beams and resonator fields, drift tube diameters must be made relatively small.

In order to obtain electromagnetic wave powers higher than are available from a single one of such klystron tubes, structures with extended dimensions normal to the electron beams have been proposed. In these cases, at least one dimension of the electron beam must be re stricted in order to achieve satisfactory coupling to the field of the circuit. This entails use of either a sheet electron beam or a multiplicity of pencil-like electron beams. However, use of a sheet beam allows the possibility of feedback of radio frequency energy between output and input resonators which can result in undesired oscillations. Devices using a multiplicity of beams in conjunction with resonant circuits have here-toforebeen suggested but have been limited to the use of only relatively few beams due to adjacent mode interference problems which in such prior devices become enhanced with each additional beam. Also, higher power levels have been obtained by combining the output of an even number of klystron tubes in a hybrid coupler to provide power for power, levels of the order of ten or more times that of a single klystron tube of the type presently cornmer-f cially available.

As a result, there exists a relatively' Also, it is desirable to obtain such power with low voltage operation to minimize power supply requirements and to reduce the radiation shielding requirements needed to minimize X-ray hazards.

It is, accordingly, an object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for generating and handling substantially high electromagnetic wave power at microwave frequencies.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for generating and handling substantially high electromagnetic wave power at microwave frequencies and including new and improved rneans for minimizing mode interference problems of the type generally encountered in multiple-beam devices.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus for generating and handling large amounts of electromagnetic wave power at microwave frequency ranges and in such a manner that mode interference problems do not severely restrict the number of electron beams employed in the power generation.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for generating and handling large amounts of electromagnetic wave power of microwave frequencies equivalent to the total power of aplurality of individual single-beam radio frequency power generating devices.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for relatively low voltage operation in the generation of large amounts of electromagnetic wave power of microwave frequencies and thereby adapted for mini: mizing problems regarding voltage breakdown and power supply and X-ray radiation shielding requirements in the operation of such apparatus.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for relatively low voltage operation in the generation of large amounts of electromagnetic wave power of microwave frequencies and thereby adapted for minimizing problems regarding voltage breakdown and power supply and X-ray radiation shielding requirements in the operation of such apparatus.

It is still another object of this invention to provide a new and improved electron discharge device comprising a single evacuated structure incorporating multiple-beamtype radio frequency power generating structures and adapted for generating and handling electromagnetic wave power at microwave frequencies with a minimum of mode interference problems and at power levels equivalent to the total power output of a comparable number of individual single-beam klystron devices.

Further objects and advantages of this invention will become apparent as the fol-lowing description proceeds and the features of novelty which characterize this invention Will be pointed outwith particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of this invention, and according to one embodiment thereof, there is provided multiple-beam radio frequency apparatus comprising input, output, and preferably at least one intermediate, longitudinally-resonant sections of transmission line pref erably in the form of longitudinally-resonant waveguides. The resonant waveguides are supported in spaced parallel relation; and extending perpendicular to and in operative association with the waveguides are at least several parallel klystron-like beam devices. Each of such devices includes a plurality of axially spaced drift tubes defining input, output, and one or more intermediate capacitive interaction gaps located in respective ones of the mentioned waveguides, an electron gun for projecting a beam of electrons through the drift tubes past the interaction gaps and a collector for collecting the electrons emerging from the last drift tube. In each waveguide the interaction gaps defined by the opposed ends of adjacent drift tubes comprise equally-spaced active capacitive elements. Also, in each waveguide and interposed midway between each pair of active elements therein is a passive, or dummy, capacitive element having a capacitance value substantially equal to that of an active element. Thus, each resonant waveguide constitutes a periodically-loaded, longitudinally-resonant section of transmission line with the periodic loading resulting from the provision therein of the alternate equally-spaced active and passive capacitive elements. Further, the periodic electrical spacing between adjacent capacitive elements and between the outermost capacitive elements and adjacent end walls in each line is made equal to A of the loaded guide wavelength at a predetermined operating frequency. Suitable means, such as an inductive coupling loop, is provided for exciting the input waveguide to establish therein a standing electromagnetic wave of the aforementioned predetermined frequency which results in the occurence of an electric field maximum at each active capacitive element in the input waveguide and a voltage node at each passive, or dummy, element. The standing electromagnetic wave thusly excited in the input waveguide velocity modulates all of the electron beams with maximum efficiency energy exchange and each of the beams becomes density modulated in a subsequent field-free drift region. The density modulated beams cooperatively excite similar standing waves in the intermediate waveguides and which results in further density modulation of the beams in subsequent drift regions. Finally, the density modulated beams cooperatively induce a corresponding amplified standing electromagnetic wave in the output waveguide. In the output waveguide also the electric field maxima occur at the active elements and the voltage and nodes at the passive elements. The electromagnetic wave energy is extracted from the output waveguide by any suitable means, such as an inductive coupling loop or an inductive output iris. The apparatus can comprise a unitary structure wherein the waveguides and beam devices comprise sections of a single sealed evacuated assembly. Alternatively, the waveguides and beam devices can comprise separate subassemblies with the waveguides constructed to carry the passive elements therein and having sockets for receiving beam devices constructed as discrete evacuated components including active capacitive gaps and which are adapted for being detachably mounted in the waveguides at locations effective for providing the mentioned predetermined periodic loading of the Waveguides. The input and output coupling means are located adjacent to the active elements in order thereby to be located in maxima field regions. I

For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIGURE 1 is a sectional view of a multiple-beam electron discharge device constructed according to one embodiment of the invention and incorporating four electron-beam-producing means;

FIGURE 2 is a stepped cross-sectional view taken along the lines 2-2 in FIGURE 1 and looking in the direction of the arrows; 7

FIGURE 3 is a cross-sectional view taken along the lines 33 in FIGURE 1 and looking in the direction of the arrows;

FIGURE 4 is an w-B diagram showing the graphical relation between the frequency of operation of a periodically-loaded waveguide and the phase shift per section of such waveguide;

FIGURE 5 illustrates diagrammatically the electric field distribution in the waveguides in the present invention when operated. in the 1r/2 mode and enables comparison of such distribution with the electric field distribution obtainable in ar/Z mode operation of a waveguide when the present invention is not employed; and

FIGURE 6 is a partially sectionalized view of another embodiment of the invention. I

Referring now to FIGURE 1, therein is shown multiplebeam radio frequency amplifying apparatus constructed in accordance with the invention. More specifically, the arrangement of FIGURE 1 is an electron discharge device in which energy from four electron beams is converted into electromagnetic wave energy and which has substantially four times the power generating and handling capabilities of a single-beam klystron of comparable dimensions. However, from the outset, it is to be understood that this invention is not limited to a device having four beams. Instead, the invention can be used in providing devices having almost any number of electron beams, the limit depending only on the impedance per beam and the fact that at some substantially large number of beams the mode separation will be so small as to make the construction of a practical operative device difficult.

The device of FIGURE 1 is constructed as a unitary evacuated envelope comprising four resonant waveguides designated 1-4 arranged in spaced parallel relation and a plurality of transversely-extending, equally-spaced cooperating klystron-like beam devices designated 5-8. In this arrangement each of the waveguides 1-4 is a shortcircuited or longitudinally-resonant section of a periodically-loaded waveguide, the specific structure and function of which will be discussed in detail hereinafter. The waveguides can have a rectangular cross-section as illustrated in FIGURES l and 2 or can be of any desired cross sectional configuration. Also, the waveguides each include end walls 9 which serve to short electrically the ends thereof and to maintain a suitable vacuum in the assembly. Further, each waveguide is provided with suitable tuning means which, as shown, can comprise sliding end-wall tuners 10 of a type well-known in the art.

The lowermost waveguide 1 in FIGURE 1 constitutes an input resonator and is adapted to be excited for having a standing electromagnetic wave established therein by any suitable radio frequency input coupling means such as an inductive loop 11 shown in FIGURES 2 and 3. In a manner similar to that well known in the klystron art, the input resonator is effectively employed to velocity modulate the beams of the devices 5-8. The uppermost waveguide 4 in FIGURE 1 constitutes an output resonator and is adapted for having an amplified electromagnetic wa/ve induced therein in a manner similar to that well known in the klystron art. Energy is extracted from the output resonator by any suitable radio frequency output means such as an inductive loop 12 shown in FIG- URE 3, Interposed between the input and output resonators 1 and 4 are intermediate resonators 2 and 3, which are shown as two in number but which can be employed in any desired number. These resonators serve to increase beam modulation and bunching efficiency in generally the same well-known manner as intermediate resonators found in the klystron art.

The beam devices 5 -8 each comprise a gun section 13 including a tubular section 114 sealed and extending reentrantly in one side of the input resonator 1 and an emitter generally designated 15 adapted for directing a beam of electrons axially through the section 14. Axially aligned with each section 14 and interconnecting the several resonators are a plurality of drift tubes 16, and axially aligned therewith and extending from the output resonator 4 is a tubular section 17 connected to a collector 18. In the described arrangement the tubular sec- .tions 14 and 17 and drift tubes 16 extend reentrantly in the several resonators to define therein reentrant active capacitive gaps or elements designated 20 which have uniform capacitance values across each waveguide. As seen in FIGURE 1, these active gaps are periodically spaced along each waveguide. In accordance with one feature of the invention there is positioned midway between each pair of adjacent active gaps in each resonator a passive,

or dummy, capacitive element 21. The outermost capacitive elements, which are the active gaps 2th in FIGURE 1, are spaced from the adjacent terminations, or short circuiting structures of the waveguides, by amounts equal to the spacing between alternate active and passive elements. It will be appreciated, however, that when end tuners are used this end spacing can be varied slightly for tuning purposes without deviating from the present invention. The passive elements are adapted for having substantially the same capacitance value as the active gaps 2.0. Also, and as seen in FIGURE 1, the passive elements can comprise posts 22 supported on one wall of each of the resonators and protruding in spaced relation toward the opposite walls for defining capacitive gaps therebetween. Various alternative structures, such as oppositely extending posts or oppositely protruding indentations in the waveguide walls, can be employed for providing the passive capacitive elements in the structure.

As seen in FIGURE 2, the input coupling loop 11 is located in the same transverse plane of the resonant waveguide 1 as one of the active gaps 20. This same relationship of coupler and an active element is provided in the output waveguide and the purpose therefor will be discussed in greater detail hereinafter in connection with the discussion of the operation of the overall apparatus.

The above-described device is surrounded by a solenoid coil 23 to provide a collimating magnetic field extending parallel to the axes of the beam devices and adapted for focussing the several electron beams therein. The entire assembly is enclosed by a casing 24 formed, for example, of a material of low reluctance, such as soft iron, to provide uniformity of the axial magnetic field in the region through which the electron beams pass. The electron guns 13 which can be located outside the casing in the manner shown can be supplied with operating potentials from any suitable sources indicated by 25 and 26 and which are well known to those skilled in the art.

The operation of the above-described multiple-beam device is as follows: A standing electromagnetic wave is established in the input resonator 1 by radio frequency energy introduced thereinto through the input coupling loop 11. This wave has electric field maxima occurring at each of the active gaps 20 and electric field minima, or nodes, occurring at each of the passive gaps 21. Electric field minima also occur at each of the end wall portions 9. The active gaps 20 comprise interaction gaps and the electrons in each of the electron beams passing across these gaps become velocity modulated in the gaps in a manner well known to those skilled in the klystron art. After passing through the drift tubes 16 for a suitable predetermined distance, the electron beams each become density modulated in accordance wth the input signals to the input resonator 1, again in a manner well known to those skilled in the klystron art. The densitymodulated electron beams, or bunches in the beams, pass successively through the gaps 20 in the intermediate resonators and the drift spaces 16 which results in greater density modulation. Thereafter, the beams traverse the gaps 20 of the output resonator 4 and cooperatively induce therein an amplified standing electromagnetic wave corresponding in form to the standing electromagnetic wave established in the input resonator 1 in amanner similar to that which is well known in the klystron art. The electromagnetic wave induced in the output resonator 4 thus has electric field maxima occurring at each of the active gaps 20 and electric field minima occurring at each of the passive gaps 2.1 and end portions 10 of the waveguide. This electromagnetic Wave energy can be extracted through the coupling loop 12 in a coaxial line. The electrons constituting the beams are then collected in the electron collectors 18.

The operation of the device and its advantages may be better understood from a discussion of the propagation loaded wave guides provided in the above-described structure. An electromagnetic wave in either of the resonators 1-4 is presented with periodically arranged capacitances in the forms of the active capacitive gaps 20 and the passive capacitive elements 21. Thus, each of the resonators li is, in effect, an electrically short-circuited section of a periodically-loaded waveguide with the periodic loading afforded by alternate active and passive gaps 20 and 21, respectively.

FIGURE 4 is an 40-5 diagram and shows the graphical relation of the phase shift per section of matched periodically-loaded waveguides as a function of the frequency of an electromagnetic wave Within such waveguides. As seen in FIGURE 4, each of the loaded waveguides has a lower limit of frequency, or lower cut-off requency, below which energy can not be propagated therethrough. As the frequency increases above the lower cut-off frequency, propagation becomes possible; and if the frequency is continuously increased above cut-off, a freq iency will ultimately be reached where the spacing between adjacent periodic capacitances in the periodicallyloaded waveguide becomes equal to half of a waveguide wavelength. At this frequency, the phase shift between adjacent capacitances is equal to 1.- radians. The reflection from a capacitance then reinforces the reflection from the immediately preceding periodic capacitance and the overall effect in a long waveguide is total reflection and no propagation. The matched periodically-loaded waveguide thus serves as a band-pass filter for frequencies between these upper and lower cut-off frequencies. The matched periodically-loaded waveguide also has pass bands and stop bands at higher frequencies, but they are of no interest for the present discussion.

While the matched periodically-loaded waveguide can support an electromagnetic wave having a frequency of any value within the pass band, and additional limitation exists when the periodically-loaded waveguide is made resonant by terminating the ends in short circuits, as is the case for the above-described resonators. Resonance occurs in the short-circuited periodically-loaded waveguides only at those frequencies at which the structure is an integral number of loaded guide half wavelengths long, and in such waveguides the total phase shift along the guides must thus be an integral multiple of 1r. In other words, resonance occurs only at frequencies at which the difference in phase of the wave at two adjacent periodic capacitances is 1rn/N where N is the number of sections into which the line is divided by the periodic capacitances and n is an integer in the interval 11:1 to n=N. Thus, the resonators 1-4 are capable of supporting electromagnetic waves only of a frequency indicated at positions 2532 of FIGURE 4, with each of these frequencies having a phase shift per section of 1r/ 8, 1r/4, 31/8, 1r/2, 51r/8, 34T/4, 71/8 and Tr radians, respectively. It is to be noted that all of these frequencies lie between the lower cut-off frequency and the upper cut-off frequency of the first pass band of the periodically-loaded waveguide.

It is known in the klystron art that maximum energy transfer between an electromagnetic wave and an electron beam occurs when the electron beam sees the greatest possible integrated electric field when passing through an interaction gap of the klystron. FIGURE 5 illustrates schematically and comparatively the electric field distributions in 1r/ 2 mode operation and with the waveguides constructed both -(1) without the advantages of the present invention and (2) in accordance with the present invention. When the teaching of the present invention is not followed qr/2 mode operation results in a field distribution wherein maximum voltages do not coincide with the interaction, or active, gaps 20 which would results in less than maximum eificiency operation. Where, however, the teaching of the present invention is followed and the waveguide is periodically loaded by alternate, equally-spaced, active and passive gaps of substantially equal capacitances the field maxima in 1r/2 operation coincide with the interaction gaps and the nodes, or field minima, coincide with the passive, or dummy gaps. This arrangement thus satisfies the requirement that each electron beam sees an electric field having a voltage maxima at the point of interaction and provides for maximum energy interchange between the beams and waves in the waveguides with resultant maximum operational efficiency. Further, reference to FIGURE 4 shows that maximum frequency separation of adjacent modes, and thus minimum mode interference problems, occurs at position 28, which corresponds to 1r/2 phase shift per section in the periodically-loaded waveguides. The justdescribed operational benefits can be obtained with the dedescribed periodic'loading provided in only the input and output resonators. However, maximum efiiciency and mode separation are better insured when the described periodic loading is provided in intermediate resonators also. Additionally, the described active and passive gap loading serves the desirable function of maintaining the phasing in the desired 1r/2 phase relationship. Thus, by including such loading in the intermediate waveguides as well as the input and output waveguides the 1r/2 phase relationship is insured through the device.

The input and output coupling loops 11 and 13 are located in the planes of active gaps 20 because of the location of longitudinal magnetic field maxima thereat. This arrangement provides for maximum interaction between these elements and thus maximum efficiencyin coupling energy into the input resonator 1 and out of the output resonator 4. If desired, other coupling means, such as coupling irises, can be effectively employed at the locations and in place of the coupling loops. Aso, the coupling means can be provided in an end wall 9 as long as it is in a plane extending through an active gap 20.

It is thus seen that the multiple-beam device of FIG- URE 1 is adapted for maintained operation in the 1r/2 mode, thereby providing assured maximum mode separation, while at the same time presenting a maximum field intensity in the resonators to each of the electron beams in the interaction region, thereby to provide maximum efiiciency in cooperative power transfer from the electromagnetic wave in the input resonator to the multiple electron beams and from the multiple electron beams to an electromagnetic wave in the output resonator. In the disclosed structure the operative cooperation of the beams and electromagnetic waves in the waveguides is such that should a beam fail, or be intentionally shut off, the output power will be decreased by essentially only that amount which that beam contributed to the operation of the device. A beam failure or shut off does not have any substantial degrading effects on the power contributions of the other beams. Additionally, the described operation is obtainable with low voltages relative to the voltages that would be required if comparable power levels were sought to be obtained with a singlebeam device. This minimizes the power supply requirements. Also, it reduces the tendency toward X-ray generation by impingement of electrons on the collector surfaces and, thus, reduces radiation shielding requirements needed to minimize X-ray hazards.

As seen in FIGURE 6, a device constructed according to the present invention need not comprise a unitary evacuated envelope including both the waveguide sections and beam devices. Instead, and .as illustrated in this figure, the waveguide sections and beam devices can comprise discrete subassemblies with the beam devices detachably mounted in, or coupled to, the waveguide sections.

Specifically, the apparatus can comprise a plurality of discrete resonant waveguide sections 35-37, having end walls 38 and tuning means 39 similar in structure and function to those described above in respect to FIGURE 1. The waveguides 35 and 37 can comprise input and output resonators, respectively, and can be provided with appropriate input and output couplers 40 and 41, respectively.

Additionally, the resonator 36 can comprise an intermediate resonator having the same function as any intermediate resonator in FIGURE 1. If desired. more than one intermediate resonator can be provided.

The resonators 3537 are provided with suitable sockets generally designated 42 adapted for receiving therein the interaction assemblies of a plurality of discrete external resonant section klystrons 43. The klystrons 43 can each comprise an evacuated device including a gun 44, tubular sections 45 and 46 and intermediately located drift tubes 47 and a collector 48. Additionally, the opposed ends of the sections 45 and e6 and the drift tubes 47 cooperate to provide interaction, or active capacitive, gaps 50. These sections are also provided with flanges 51 between which are suitably sealed cylindrical ceramic R.F. Windows 52.

Provided in each of the waveguides 35 and 37 and located midway between each adjacent pair of interaction gaps is a passive, or dummy, capacitive gap or element 53. Also, the spacing of the waveguide terminations, or short circuits, relative to the outermost capacitive gap is essentially the same as the spacing between adjacent interaction and dummy gaps. The interaction gaps 50 and the dummy capacitive gaps 53 provide essentially the same periodically-loaded waveguide structure as that described with reference to FIGURES 1-3. Also, the overall assembly can, be provided with an identical solenoid structure; and the purpose, function and operational benefits of the apparatus of FIGURE 6 can be identical to those of the device of FIGURES 1-3.

While the invention is thus shown and the mode of operation of specific embodiments have been described, the invention is not limited to these shown embodiments. Instead, the foregoing will suggest to those skilled in the art modifications which will lie within the scope of the invention. For example, the invention is not limited to use in a device using four electron beams, but can be used in a device having almost any desired number of electron beams. Also, the input and output resonators need not necessarily take the shape of a straight section of waveguide, but can instead take the shape of a curved section of waveguide, if desired. The resonators need not be conventional closed waveguides either, but can comprise resonant sections of any form of transmission line. The active gaps need not be the interaction gaps of beam-type devices and the present concept of periodically loading resonant waveguides with alternate active and passive gaps is applicable where other types of active gaps are employed. Another such type of structure is disclosed and claimed in copending US application S.N. 173,703 of R. A. Dehn filed concurrently herewith and assigned to the same assignee as the present invention and wherein space-charge control devices are employed. Further, the transmission line in the present structure can comprise large-area planar conductors with the lines of periodically arrayed active and passive gaps extending in a plurality of directions providing, for example, parallel rows of arrays such as those discussed above and illustrated in FIGURES 1 and 6.

Further, while the present invention affords increased operating efficiency, maximum mode separate at 1r/2 mode operation and serves to maintain operation in the desired 1r/2 phase relationship the disclosed type of structure can, if desired, be operated to produce high output power in a number of discrete frequency intervals centered about several of the other normal resonant modes of the system. For example, the device can be constructed according to the present invention and to include a substantial number of electron beam devices. If all such beams were operated at all frequencies of operation the overall efficiency would be relatively low because only some of the beams would be located at electric field 'maxima while others would be located at field minima and would contribute nothing to the output power. However, very high power output can be obtained with desired high efficiency by predeterminedly programing, or selectively operating, the beams to match the radio frequency mode pattern in each band of frequencies and thus avoiding operation of the beams which do not contribute to power output in those particular frequencies. For other than 1/2 mode the output power will be less than N times the capability of one beam; however, much more than that of a single-beam device. By programing the beam power to suit the resonant modes, the output frequency can be rapidly changed with minimum degradation of efficiency. It is thus intended that the invention "be limited in scope only by the appended claims.

Still further, in the disclosed structure the individual interactions or outputs of all beams are phase-locked because the fields are very tightly coupled throughout the resonator. This advantage of strapping does not exist in a system wherein outputs of discrete klystrons are combined externally.

Also, the use of a multipoint drive and a particular pacitive elements positioned midwaybetween adjacent ones of said several active elements, the active elements mode in a multimode resonator has an important advantage with regard to klystron harmonic output. Specifically, current bunches arriving at a klystron output gap are ordinarily extremely rich in harmonic content. In a single resonant cavity, for harmonic power to be developed it is only necessary to have impedance present at the harmonic frequencies. In the presently-disclosed multiple-beam structure, however, in addition to this impedance requirement, there also is a phase requirement that must be satisfied to obtain harmonic output. In this case harmonic generation requires not only that the harmonic frequency occur in a higher passband at a resonance of the loaded circuit, but also that the phase shift per section be harmonically related to that of the fundamental input signal. Minimum harmonic output can be achieved by designing the structure so that harmonic frequencies occur in the stop bands of the circuit which minimum output would be significantly less than that of a single beam klystron of the same total fundamental output.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A multiple beam radio frequency apparatus comprising at least a pair of spaced resonant sections of transmission line, each periodically loaded by an array of plural alternate active and passive capacitive elements of comparable capacitance values, the active elements of each section constituting interaction gaps and being aligned with respective elements of the other section,

input means for establishing in one of said sections a standing electromagnetic wave having electric field maxima occurring at each said active elements and minima at each said passive elements therein, said passive elements being operative on said wave to provide a predetermined phase condition, means directing electrons successively across the respective interaction gaps of first said 7 One and then the other section, whereby an electromagnet- 'ic wave is induced in said other section corresponding in form to said wave in said one section and having electric field maxima and minima occurring, respectively, at said active and passive elements, and output means for extracting radio frequency energy from said other section.

2. A multiple beam radio frequency apparatus accord ing to claim 1, wherein at least one intermediate resonant section is interposed between said pair of sections in interacting relation with said electrons and includes the same periodic loading as said pair of sections.

3. A multiple beam radio frequency apparatus according to claim 1, wherein said input and output means are each located in a plane extending through an active element for thereby being disposed in a region of field maxima.

4. A multiple beam radio frequency apparatus comprising at least a pair of spaced resonant sections of a transmission line, each being periodically loaded by a linear array of several active capacitive elements and a separate plurality of passive capacitive elements of comparable capacitance values, one of each said passive caof each section constituting interaction gaps and being aligned with respective elements of the other section, means for establishing in one of said sections a standing electromagnetic wave having electric field maxima occurring at each said active elements and minima at each said passive elements therein, said passive elements being operative on said wave to provide a predetermined phase condition, means for projecting discrete electronbeams across said interaction gaps in first said one section and then the other said sections and including drift space defining means located along said beams between said interaction gaps, whereby an electromagnetic wave is in duced in said other section corresponding to said wave in said one section and having electric field maxima and minima occurring, respectively, at said active and passive elements, and means for extracting radio frequency energy from said other section.

5. Multiple beam radio frequency apparatus comprising at least a pair of spaced resonant waveguides each being periodically loaded by at least several active capacitive elements and separate plural passive capacitive elements of substantially equal capacitance value, said passive capacitive elements being positioned substantially midway between adjacent ones of said several active elements, the active elements of each waveguide constituting interaction gaps and being aligned with respective elements of the other waveguide, means for establishing in one of said waveguides a standing electromagnetic wave having electric field maxima occurring at each said active elements and minima at each said passive elements there in, said passive elements being operative on said wave to provide a predetermined phase condition, means for directing electrons successively across the respective inter action gaps at first said one and then the other said waveguides,. whereby an electromagnetic wave is induced in said other waveguide corresponding to said wave in said one waveguide and having electric field maxima and minima occurring, respectively, at said active and passive elements, and means for extracting radio frequency energy from said other waveguide.

6. Multiple beam radio frequency apparatus according to claim 5, wherein said means for directing electrons comprises means for projecting discrete electron beams across said interaction gaps and includes drift-space defining means located along said beams between said interaction gaps.

7. Multiple beam radio frequency apparatus compris ing at least a pair of spaced resonant sections of transmission line each being periodically loaded with separate alternate active and passive capacitive elements of substantially equal values, each said element spaced the length of wave energy from an adjacent element in said sections when said sections are loaded at a predetermined operating frequency, the active elements of each section constituting interaction gaps and being aligned with respective elements of the other section, means for establishing a standing electromagnetic wave of said predetermined frequency in one of said sections, said passive elements being operative on said wave to provide a predetermined phase condition, means for directing electrons successively across the respective interaction gaps of said one and then the other of said sections, whereby an electromagnetic wave is induced in said other section corresponding in form to the wave of said one section, and means for extracting energy from said other section.

8. Multiple beam radio frequency apparatus comprising at least a pair of spaced resonant waveguides each being periodically loaded by separate several equallyspaced reentrant members defining interaction capacitive gaps and several equally spaced capacitive elements defining passive capacitive gaps, said gaps being of substantially equal capacitance values, said gaps being electrically spaced the length of wave energy in said waveguides when said waveguides are loaded at a predetermined op erating frequency, in each waveguide alternate ones of said gaps constituting interaction and passive gaps and being aligned with respective gaps in the other waveguide, means for establishing a standing electromagnetic wave in one of said waveguides at said predetermined frequency,

said passive capacitive gaps being operative on said wave in said waveguide to provide a predetermined phase condition, means for directing discrete electron beams across the respective interaction gaps of said one and then said other waveguide, including drift space defining means located along said beams between said interaction gaps, whereby an electromagnetic wave is induced in said other waveguide corresponding in form to the wave in said one waveguide, and means for extracting energy from said other waveguide.

9. Multiple beam radio frequency apparatus according to claim 8, wherein at least one intermediate resonant waveguide is interposed between said pair of waveguides for enabling an interacting relation of an electromagnetic Wave therein with said electron beams and includes the same periodic loading structure as said pair of waveguides.

10. Multiple beam radio frequency apparatus according to claim 8, wherein said input and output means are each located in the same transverse planes through said waveguides as interaction gaps therein.

11. A multiple-beam electric discharge device comprising an evacuated envelope including as sections thereof at least input, output, and an intermediate resonant waveguides arranged in spaced parallel relation, said waveguides each being periodically loaded by a Separate straight line array of several equally-spaced members defining plural alternate interaction active gaps and plural passive gaps which gaps are axially aligned with respective gaps in the other waveguide, said active and said passive gaps having substantially equal capacitive values, adjacent gaps in each said waveguides being electrically spaced A the length of wave energy therein when said waveguide is loaded at a predetermined operating frequency, means for projecting at least several discrete elec tron beams transversely successively across said input and output waveguides at said interaction gaps and including drift tubes interconnecting said interaction gaps, means for establishing a standing electromagnetic wave in said input waveguide for interacting with said beams in said interaction gaps therein for velocity modulating said beams to effect space charge density modulation in said drift tubes, said passive gaps being operative on said wave to provide a predetermined phase condition, whereby said beams are adapted for inducing in said output waveguide anelectromagnetic wave corresponding in form to that in said input waveguide, and means for extracting energy from said output waveguide.

12. A multiple-beam klystron apparatus comprising a least input, output, and an intermediate resonant waveguides arranged in spaced parallel relation, said waveguides each including a straight line array of at least four electric discharge device sockets, and at least three passive capacitive gap elements disposed in said waveguides midway in alternate relationship between each adjacent pair of said sockets, a plurality of external resonant section beam devices each adapted for projecting a discrete electron beam transversely successively across said waveguides and including reentrant interaction gaps disposed in said waveguides at said sockets and drift tubes interconnecting said interaction gaps, adjacent interaction gaps and passive elements being of substantially equal capacitance values and electrically spaced the length of wave energy in said waveguides when said waveguides are loaded at a predetermined operating frequency, means for establishing a standing electromagnetic wave in said input waveguide for interacting with said beams at said interaction gaps therein for velocity modulating said beams to effect space charge density modulation in said drift tubes, said passive gaps being operative on said wave to provide a predetermined phase condition, whereby said beams are adapted for inducing in said output Waveguide an electromagnetic wave corresponding in form to that in said input waveguide, and means for extracting energy from said output waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,353,742 7/1944 McArthur 3155.16 2,458,556 1/1949 Bowen 3155.46 X 2,657,329 10/1953 Wathen 3155.29 X 2,920,229 1/1960 Clarke 3155.16

FOREIGN PATENTS 686,830 2/ 1953 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner.

S. CHATMAN, Assistant Examiner. 

1. A MULTIPLE BEAM RADIO FREQUENCY APPARATUS COMPRISING AT LEAST A PAIR OF SPACED RESONANT SECTIONS OF TRANSMISSION LINE, EACH PERIODICALLY LOADED BY AN ARRAY OF PLURAL ALTERNATE ACTIVE AND PASSIVE CAPACITIVE ELEMENTS OF COMPARABLE CAPACITANCE VALUES, THE ACTIVE ELEMENTS OF EACH SECTION CONSTITUTING INTERACTION GAPS AND BEING ALIGNED WITH RESPECTIVE ELEMENTS OF THE OTHER SECTION, INPUT MEANS FOR ESTABLISHING IN ONE OF SAID SECTIONS A STANDING ELECTROMAGNETIC WAVE HAVING ELECTRIC FIELD MAXIMA OCCURRING AT EACH OF SAID ACTIVE ELEMENTS AND MINIMA AT EACH SAID PASSIVE ELEMENTS THEREIN, SAID PASSIVE ELEMENTS BEING OPERATIVE ON SAID WAVE TO PROVIDE A PREDETERMINED PHASE CONDITION, MEANS DIRECTING ELECTRONS SUCCESSIVELY ACROSS THE RESPECTIVE INTERACTION GAPS OF FIRST SAID ONE AND THEN THE OTHER SECTION, WHEREBY AND ELECTROMAGNETIC WAVE IS INDUCED IN SAID OTHER SECTION CORRESPONDING IN FORM TO SAID WAVE IN SAID ONE SECTION AND HAVING ELECTRIC FIELD MAXIMA AND MINIMA OCCURRING, RESPECTIVELY, AT SAID ACTIVE AND PASSIVE ELEMENTS, AND OUTPUT MEANS FOR EXTRACTING RADIO FREQUENCY ENERGY FROM SAID OTHER SECTION. 